Referring to U.S. Pat. No. 3,984,887, as one example of a conventional collapsible boat, the right and left sides of the boat can be folded over a bottom of the boat and also can be unfolded back to form a boat shape. The boat has a beam which retains the above-mentioned unfolded condition, and also serves as a seat for occupants.
The overall appearance of the boat body is spindle-shaped with an oval cross section. The body is made of flexible synthetic resins, by blow molding. Right and left sides of the boat are made of flexible material so that they can be folded over the boat bottom and then unfolded. A projection is provided at each inner side of the boat. The beam is installed between the projections to retain the unfolded condition of the sides. The boat has a spindle-shaped hollow shape when the sides are folded over the bottom so that the beam can be stored inside the boat.
In that conventional collapsible boat, the beam and the body are not firmly linked, so the beam may tend to shift in response to vibration. Further it is not easy to unfold and set up the sides from the collapsed condition, because the beam must firstly be taken out from inside the body, and then, while the sides are held in an unfolded condition, the beam must be inserted between the projections. Thus, an awkward setting-up operation constitutes a problem to be solved.
Also, the conventional collapsible boat is structured to be propelled by oars or a motor, not by sails.
There is also a disadvantage in the conventional collapsible boat in that the bow easily rises above the water surface due to its light body weight when using an outboard motor at comparative high speed. That disadvantage is likely to occur when the occupant is seated at the stern of the boat or when the occupant's gear is stored in an improper manner.
An additional disadvantage is that the beam, serving as a seat, must remain at a determined position, so that the occupants cannot move the seat location in order to balance the body. Conversely, if the occupants choose to occupy positions which achieve a proper balance, they may not be able to sit on the seat.
And although certain articles, such as eyelets can, together with the beam be stored, within the boat body, such articles may not be housed in a stable condition, as the housed position of the beam cannot be set at a fixed position.